import java.util.Arrays;
import java.util.Scanner;

public class T781 {
    public static void main(String[] args) {
        int[] data = new int[200];
        for (int i = 0; i < 200; i++)
            data[i] = 4 * i + 6;
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        System.out.println(Arrays.binarySearch(data,n));
    }
}
